Summary/Abstract: Projections indicate that over 50% of the world?s population will have myopia by the year 2050. To develop successful myopia prevention programs, it is critical to first discern the optical image formation and visual processing characteristics in children who develop myopia. Considerable evidence points to the quality of the visual image and absence of blur as the main drivers for normal ocular growth and emmetropization. Human eyes have complex optical, retinal and visual processing structures and functions. Any and all of these factors affect the perception of image quality, and may, therefore, be catalysts of the failure to control ocular elongation and myopia development in children. To better understand the mechanism(s) for the development of myopia, these factors ought to be measured in the same children over a longitudinal period, prior to and after the onset of myopia. The immediate objective of this prospective longitudinal study is to tease out retinal image quality and visual processing factors that may contribute to the development of myopia. We will recruit two groups of young children, limiting eligibility to only children who are either at high risk or low risk to develop myopia during the duration of the study. The following factors will be assessed in each child at 6-month intervals over a period of 3 years: (1) Optical quality of the image formed at the retina. We predict that: dynamic accommodation is less stable prior to myopia development, causing degraded retinal images; and children who develop myopia will show degraded image quality across the retina. (2) Retinal responses to image blur will be measured using pattern electroretinography while subjects observe images blurred with various types and amounts of simulated optical blur. We predict that children with impaired retinal responses will develop myopia. (3) Processing of blur will be measured using blur detection and discrimination thresholds and contrast sensitivity functions across the visual field to the same types of image blur described in (2). We predict that visual processing of blur will be impaired in children who develop myopia. We will create individual models of interactions between the three measures: optical image quality, retinal function and visual processing. We predict that deficits in retinal image quality, retinal function and visual processing or their interactions lead to a cycle of abnormal representation of blur, which would in turn cause the development of myopia. Understanding the signals that activate myopia development will have a significant impact and will help us and other researchers to design future clinical studies for the prevention and control of myopia. Knowledge of the mechanism(s) for myopia development is essential for the design of effective individualized interventions in children at risk for myopia, which can be assessed in subsequent clinical trials.